Conventionally, a fuel supply system which supplies fuel to an engine is equipped with a high-pressure pump. The high-pressure pump is generally provided with a plunger which reciprocates along a camshaft. When the plunger slides down from its top dead center to its bottom dead center, a fuel in a fuel gallery is suctioned into a compression chamber (suction stroke). When the plunger slides up from the bottom dead center to the top dead center, a part of the low-pressure fuel is returned to the fuel gallery (metering stroke). Then, after a suction valve is closed, when the plunger further slides up, the fuel in the compression chamber is compressed (compression stroke).
Generally, the fuel is supplied to the fuel gallery through an inlet and a supply quantity of the fuel depends on a pump performance of a low-pressure pump disposed upstream of the high-pressure pump. When the engine speed increases and the rotational speed of the camshaft is increased, the plunger of the high-pressure pump reciprocates at high speed. It is likely that the fuel supplied through the inlet does not fill the compression chamber enough in the suction stroke. In order to solve such a problem, JP-2006-200407A (US-2006-0159555A1) and JP-2008-525713A, for example, show a high-pressure pump which performs a pumping function to discharge the fuel into the fuel gallery even while the plunger slides down from the top dead center to the bottom dead center.
Besides, in the metering stroke, a pressure pulsation arises due to a low-pressure fuel discharged from the compression chamber to the fuel gallery. Japanese patent No. 4036153 (US-2005-0019188A1) and JP-2008-286144A (US-2008-0289713A1), for example, show a high-pressure pump provided with a pulsation damper in the fuel gallery to reduce the pressure pulsation in the fuel gallery. In the high-pressure pump shown in Japanese patent No. 4036153 (US-2005-0019188A1), a space defined between one surface of a pulsation damper and a bottom wall surface of a housing communicates with an inlet and a compression chamber. In the high-pressure pump shown in JP-2008-286144A (US-2008-0289713A1), a space defined between a support plate supporting a pulsation damper and a bottom wall surface of a housing communicates with an inlet and a compression chamber.
However, in the high-pressure pump shown in JP-2006-200407A and JP-2008-525713A, since the fuel flow in the fuel gallery is not considered, the above pumping function of the plunger is not effectively achieved, so that the suction quantity of the fuel into the compression chamber may be insufficient. Further, in the metering stroke, since a flow velocity of the low pressure fuel discharged from the compression chamber into the fuel gallery is very fast, it is likely that the pressure pulsation is not attenuated sufficiently by the pulsation damper and the fuel leaks from an inlet to a low-pressure fuel pipe in the high-pressure pump disclosed in Japanese patent No. 4036153.
In the high-pressure pump disclosed in JP-2008-286144A, the low-pressure fuel discharged from the compression chamber into the fuel gallery collides with a supporting member of the pulsation damper, so that a flow direction of the fuel is changed transversely. It is likely that the pressure pulsation is not attenuated sufficiently by the pulsation damper and the fuel leaks from an inlet to a low-pressure fuel pipe. When the pressure pulsation is transmitted to the low-pressure fuel pipe, the low-pressure fuel pipe may be vibrated to generate a noise from a fixing member which supports the low-pressure fuel pipe. Such a vibration may be transmitted to a vehicle body through the fixing member. Also, it is likely that the fixing member itself may be damaged.